This invention relates to a safety device for an undersea vehicle using lithium batteries. More particularly, this invention is to a pressure relief valve system for venting Li/SO2 vapors created by lithium batteries to prevent damage to an undersea vehicle.
The long shelf-life and higher watt-hours per unit volume of lithium batteries as compared to other contemporary batteries is well known. Marine designers have included lithium batteries in unmanned submersibles where a compact high-power electrical source is needed to produce sufficient power for prolonged operations at considerable depth.
One of the major consequences of using high power density lithium batteries, however, is that they can produce considerable amounts of pungent and toxic Li/SO2 vapors at temperatures above their venting point of about 200° F. Such temperatures could be created in the event of a shipboard fire in either the magazine where the submersibles are stored or in an adjacent compartment. One instance where ambient temperatures increased from 200° F. to about 251° F. caused one lithium-battery equipped undersea vehicle to have its nosepiece portion separate from its body portion. When Li/SO2 vapors reached oven temperatures of about 251° F., internal pressures in the range between 100 psi and 200 psi were created by the Li/SO2 vapors in the interior of the vehicle and the nose portion separated. Irrespective of the advantages of having a lithium battery power source aboard, the undersea vehicle could not be used until this damage was repaired.
Thus, in accordance with this inventive concept, a need has been recognized in the state of the art for a reliable internal pressure relief valve system for an undersea vehicle containing lithium batteries in an undersea vehicle capable of diving to considerable depths.